Inhibition of corrosion using alkyl aryl ketones

ABSTRACT

CORROSION OF METALS BY AQUEOUS ACIDIC SOLUTIONS IN A NON-OXIDIZING ATMOSPHERE IS MARKEDLY INGIBITED BY THE PRESENCE OF A LOWER ALKYL ARYL KETONE. A PARTICULARLY EFFECTIVE INHIBITOR OF THIS TYPE IS METHYL BETA-NAPHTHYL KETONE. CORROSION OF CHEMICAL AND PETROLEUM PROCESS EQUIPMENT HANDLING HYDROCARBON STREAMS CONTAINING ACIDIC GASES AND WATER VAPOR IS MINIMIZED BY THE PRESENCE OF THE CORROSION INHIBITOR OF THIS INVENTION.

3,640,895 INHIBITION OF CORROSION USING ALKYL ARYL KETONES Zisis AndrewForoulis, East Orange, N.J., assignor to Esso Research and EngineeringCompany No Drawing. Filed July 2, 1968, Ser. No. 741,869 Int. Cl.C23f11/04, 11/12 US. Cl. 252396 15 Claims ABSTRACT OF THE DISCLOSURECorrosion of metals by aqueous acidic solutions in a non-oxidizingatmosphere is markedly inhibited by the presence of a lower alkyl arylketone. A particularly effective inhibitor of this type is methylbeta-naphthyl ketone. Corrosion of chemical and petroleum processequipment handling hydrocarbon streams containing acidic gases and watervapor is minimized by the presence of the corrosion inhibitor of thisinvention.

BACKGROUND OF THE INVENTION This invention relates to the prevention ofcorrosion of metals by aqueous acidic solutions, and more particularlyto the prevention of corrosion of chemical and petroleum processequipment which is subjected to corrosive attack by aqueous acidicsolutions in a non-oxidizing atmosphere as a result of condensation ofwater containing dissolved acidic substances.

Various acidic substances which are present in petroleum refiningoperations cause corrosion of metals with which they come in contact.Examples of destructive inorganic compounds include hydrochloric acid,sulfuric acid, sulfur dioxide, and hydrogen sulfide. Organic compoundscausing corrosion include acetic acid, phenolic compounds, naphthenicacids, and aliphatic and naphthenic organic chlorides. Corrosion-causingacids enter the hydrocarbon process streams in petroleum refineries invarious ways. For example, crude oils generally contain naphthenicacids. The organic chlorides do not usually occur naturally in crudeoil, but are sometimes added by producers for removal of parafiindeposits in producing wells and pipelines. These tend to hydrolyze inthe presence of water to produce hydrochloric acid. Hydrogen sulfide isformed in catalytic desulfurization processes using hydrogen, in whichvarious hydrocarbon feedstocks including virgin and cracked naphthas, aswell as gas oils, containing such impurities as mercaptans, disulfides,and thiophenes, are catalytically reacted with hydrogen in order toreduce their sulfur content. Sulfuric acid and sulfur dioxide are bothprocessing reagents, the former being used as an alkylation catalyst andthe latter as an extractant for the removal of aromatics fromhydrocarbon feedstocks. Hydrochloric acid and hydrogen chloride mayresult from several sources, including the hydrolysis of organicchlorides, hydrolysis of salt which is mixed with crude oil as a resultof the use of brine in oil production operations, and as a result ofhydrolysis of chlorine gas which is used in the regeneration of platinumreforming catalysts.

Acidic substances such as the foregoing will cause severe corrosion ofthe metals from which conventional petroleum refining equipment isconstructed. Carbon steels, such as 1020 carbon steel containing 0.2%carbon, are used predominantly as materials of construction. While itwould be possible to fabricate refinery equipment from steels which areless prone to corrosive attack, such as stainless steel and specialalloy steels, the cost of such equipment would be inordinately high andwould make any proces being conducted with such equipment uneconomical.

United States Patent Corrosion in petroleum process streams isparticularly troublesome in equipment, such as condensers and heatexchangers, where condensation of water takes place. Water vapor isinvariably present, both in hydrocarbon process streams and inregenerator gas streams, as is well known. When this water condenses,acidic gas present in the process stream, such as hydrogen chloride,hydrogen sulfide, sulfur dioxide, and carbon dioxide, dissolve in thecondensate and attack metal equipment. Such attack occurs in hydrocarbonprocess streams containing only trace amounts of oxygen or none at all,since the metal is oxidized by the hydrogen ions of the acid.

The overhead stream from an atmospheric pipestill is one example of apetroleum process stream containing acidic gases. Such a streamgenerally contains hydrogen chloride as well as organic chlorides. Uponcondensation of this overhead stream, hydrogen chloride is dissolved inthe water condensate and the qunatity of hydrogen chloride is augmentedby hydrolysis of a portion of the organic chlorides present. Thiscondensate attacks the condenser surfaces.

Another location where corrosion may occur is on the downstream side ofa hydrotreating unit. The effluent from a hydrotreater may contain watervapor, hydrogen chloride, and hydrogen sulfide. In typical operationsthis eflluent is condensed and the hydrogen sulfide removed. Corrosionis prone to take place in the condenser and the hydrogen sulfidestripper.

Acidic atmopheres are also found frequently during the regeneration ofcatalyst for hydroforming and other catalytic hydrogenation processes.It is necessary to prevent corrosion as a result of these acid gaseswhile at the same time avoiding any significant adverse effect oncatalyst activity as a result of contact of the catalyst with acorrosion inhibitor. This is particularly important in the case ofhydroforming catalysts where the catalysts are expensive and where it isextremely crucial, from 'a process economy point of view, to extend thecatalyst life as long as possible.

One possible technique for inhibiting corrosion by acids is toneutralize the acid with a base. However, such a solution would not bepractical because there is a tremendous daily throughput of feed streamsthrough petroleum or chemical processes which contain acidic materials,thereby requiring a correspondingly large amount of base forneutralization. A further problem arises from the fact that the mostlikely bases for use in such neutralization would be either organicnitrogen compounds or ammonia. Nitrogen, however, is a severe poison formany petroleum conversion catalysts such as reforming catalysts. Its usewould, therefore, be contraindicated in any fluid stream which wouldeventually contact such conversion catalysts. It is thus evident that ameaningful answer to the problem facing the petroleum industry would notbe based on neutralization or removal of the acidic corrosive agents inthe feed stream since such techniques would either be prohibitivelyexpensive or would result in deactivation of reforming catalysts.Instead, it is necessary to provide a corrosion inhibitor whoseeffectiveness does not depend on neutralization of acid present andwhich does not adversely affect the catalyst to any significant degree,if at all.

can be inhibited to a considerable extent by the presence of a loweralkyl aryl ketone having the formula where Ar is an aryl radicalcontaining a maximum of two rings and R is a lower alkyl radicalcontaining from 1 to about 4 carbon atoms. Ar is preferably a bicyclicaryl radical such as beta-naphthyl or alpha-naphthyl. In a. preferredembodiment of the invention Ar is betanaphthyl and R is methyl.Compounds of the above formula are particularly useful in inhibitingcorrosion by aqueous acids in non-oxidizing atmospheres.

DETAILED DESCRIPTION OF THE INVENTION A preferred corrosion inhibitoraccording to this invention is methyl beta--naphtha ketone, which hasthe formula ,-oo1-Ii k Other alkyl aryl ketones can also be usedeffectively as corrosion inhibitors. Such compounds includeacetophenone, ethyl phenyl ketone, methyl alpha-naphthyl ketone, methylortho-hydroxyphenyl ketone, methyl para-hydroxyphenyl ketone, methylcresyl ketone, and methyl 5-hydroxy-2-naphthyl ketone, and ethylbeta-naphthyl ketone. Compounds in which the aryl radical contains morethan 2 rings are generally not useful since such compounds ordinarilyhave water solubilities too loW to provide an effective corrosioninhibiting concentration. The presence of long chain alkyl substituentswhich markedly decrease solubility should also be avoided. The presenceof ring substituents, such as hydroxy, which tend to increase watersolubility is frequently desirable, since some compounds conforming tothe above general formula in which neither the alkyl nor the arylradicals are substituted have water solubilities which are too low formaximum effectiveness as corrosion inhibitors. On the other hand,compounds having a substantial water solubility are also poor inhibitorsfor preventing corrosion by acids. Best results are obtained withcompounds which are substantially, but not completely, water insoluble.

The inhibitors of this invention may be used elfectively in Widelyvarying concentrations. Effective inhibition is obtained inconcentrations ranging from about moles per liter (m./l.) up to about0.5 m./l. in the aqueous acidic phase. Actually, there is no upper limiton the effectiveness of the inhibitors of this invention, and themaximum concentration is limited only by the solubility of the compound.However, concentratons in excess of 0.5 m./l. do not give inhibitoryaction substantially greater than that obtained at concentrations under0.5 m./l.

The ketones of this invention can be used eifectively in oxidizing,inert, or reducing atmospheres. These inhibitors are well suited for usein reducing atmospheres such as those encountered in petroleum processstreams. A significant advantage of these inhibitors in petroleumprocessing is that they do not poison platinum or palladium catalysts,which are poisoned by nitrogen and sulfur compounds. However, theketones of this invention may also be used elfectively in environmentswhere oxygen is present. Ketones have an advantage over aldehydes ascorrosion inhibitors where oxygen is present, since aldehydes are proneto oxidation while ketones are more stable to oxidation.

Any metals which are subject to acid attack can be protected with theinhibitors of this invention. These inhibitors are particularly usefulfor protection of ferrous metals, and especially low carbon steel, suchas 1020 carbon steel (containing 0.2% carbon). Low carbon steels areideal for construction of petroleum processing equipment from thestandpoint of cost and other significant qualities such as strength andtheir ability to withstand the process stream temperatures. Theprincipal drawback to low carbon steel is its susceptibility to acidcorrosion, and problems arising from this are substantially obviated bythe use of the inhibitors of this inventioni Non-oxidative corrosion byacids is ordinarily a problem where the pH of the acidic solution isabout 4 or lower. The ketone inhibitors of this invention offerexcellent protection even in solutions which are decidely on the acidside, e. g., those having a pH of l or lower.

A few types of apparatus used in the petroleum proccessing industry willbe cited as examples of apparatus which may be protected againstcorrosion according to this invention. One such type of apparatus is theregeneration circuit used in hydroforming. It is necessary inhydroforming to use a catalyst having a small chloride content. Duringregeneration coke is burned from the catalyst, producing an effiuentwhich has a fair concentration of CO and small quantities of S0 ,and S0During this step, the chlorides to be found in the gas vapor willincrease due to an increase in water content of the gas which serves tostrip chlorine olf the catalyst. The second step is to remove any waterleft on the catalyst. This means thorough drying of the flue gas, whichis a mixture of nitrogen, CO CO, S0 S0 and HCl. After most of the waterhas been removed, chlorination is started in a manner such that chlorinewill be progressively absorbed by the catalyst. During the subsequentrejuvenation of the catalyst to rearrange the crystal structure, somechlorine will still be carried over with the flue gas. The last step inthe regeneration operation is purging the stream With nitrogen, an inertgas, to remove air and finally pressure up with hydrogen. The inhibitorof the instant invention is injected into the hydroformer regenerationgas stream either continuously throughout the regeneration cycle or byintermittent high rate injection of inhibitor at the same total amountper regeneration cycle. The presence of the inhibitor serves to reduceor minimize corrosion in heat exchange equipment and transfer lineswhere water condensate, containing the acidic components mentionedpreviously, accumulates. The inhibitor compound is adsorbed on the metalsurface and minimizes corrosion by markedly lowering the rate ofcorrosion reactions. As indicated earlier, the prseence of alkyl arylketones, preferably in the absence of oxygen, serves to inhibit thecorrosion effects of various acid base corrosion causing substances. Aninert gas, e.g., nitrogen, is present and, in addition, corrosivesubstances such as hydrogen sulfide, hydrochloric acid, and sulfuricacid are present. The addition of an alkyl aryl ketone serves tominimize corrosion with no adverse elfect on the platinum or palladiumcatalyst. Another area where corrosion in an inert atmosphere iswidespread and has a deleterious effect is hydrotreating. Substantialquantities of hydrogen sulfide are produced in the hydrotreater byreduction of sulfur compounds such as mercaptans, disulfides, andthiophene. This causes corroslon in the presence of Water condensate.Also present is hydrogen chloride, which may result from thedecomposition of organic chlorides such as carbon tetrachloride andtrichloroethylene in the process stream, or from the hydroformer treatgas which contains HCl from decomposition of the chlorine treatedcatalyst base. In any event, the hydrotreater effiuent condenser andother overhead equipment has been plagued with problems instigated bythe presence of hydrogen chloride. Again, corrosion is greatly reducedby the injection of an aryl alkyl ketone into the process stream. Thefact that the ketones of this invention do not poison platinumcatalysts, as do inhibitors containing nitrogen or sulfur, is importantbecause the hydrotreater efiluent is frequently passed through aplatinum catalyst bed in a hydroformer, and in those cases it isimperative to avoid corrosion inhibitors which could poison the platinumcatalyst.

A significant advantage of the use of corrosion inhibitors is that it ispossible to use inexpensive construction materials such as low carbonsteel, instead of costly corrosion resistant alloy steels which wouldrender the cost of the process prohibitive.

While ferrous metals have been cited as an illustrative example ofmetals which can be protected according to this invention, it should beunderstood that other metals and alloys, such as nickel, zinc, brass,and copper, may also be protected. While copper is more resistant toacid attack in a non-oxidizing atmosphere than the other metals andalloys mentioned, nevertheless it may be prone to slight attack bystrong acids, and such attack is mitigated by alkyl aryl ketone.

The problem of corrosion attack is most severe in those units, such ascondensers, heat exchangers, and transfer lines, where water condenses.The acid gases present in the process stream are dissolved in thecondensate, and attack the metal process equipment. It has been foundthat the corrosion inhibitors herein are efiective under the entiretemperature range in which water is present in the liquid phase. Sincesome processes are run at high pressure, the actual temperature may beconsiderably above the atmospheric boiling point of water; nevertheless,the inhibitors do not lose their effectiveness at such temperatures.Likewise, they remain efiective at low temperatures down to 32 F.

The inhibitor is preferably injected into the process stream just ashort distance upstream for best results. This mitigates loss of theinhibitor, and also protects the inhibitor from decomposition from hightemperatures which prevail in some units of process streams.

While the mechanism for the inhibiting action of alkyl aryl ketones suchas methyl beta-naphtha ketone is not completely understood, thefollowing explanation is offered for the purpose of illustration and asan aid in understanding the invention, and should not be taken aslimiting the scope of the invention in any manner. The corrosionadditive is believed to be adsorbed on the metal surface in the form ofa continuous or nearly continuous thin film. This film would serve toinhibit any chemical or electro-chemical interaction between the acidiccorrosive material in solution and the metal surface. The very smallquantities of inhibitor that are utilized to form this thin film are notbelieved to undergo any significant chemical reaction with the acidiccorrosive material. Thus, only small amounts of additional inhibitorwould be necessary to maintain long term protection on metal surfaces,these additions being possibly necessitated by attrition losses due tophysical interactions of the flowing stream with the film.

As previously noted, the corrosion inhibitor should not be markedlywater soluble, nor should it be substantially completely insoluble. Inshort, the water solubility must be enough to establish an effectiveconcentration, which as earlier noted is generally at least m./l. in theaqueous acidic phase.

The present invention will be more fully understood with reference tothe following specific examples. It is understood that these examplesare illustrations of specific embodiments of this invention and are notto be taken as limitations.

Example 1 This example illustrates the effectiveness of methylbetanaphthyl ketones as an inhibitor of acid-induced corrosion of 1020carbon steel exposed to 0.1 N hydrochloric acid, which has a pH of 1.Corrosion rates were measured by weight losses, carbon steel specimenshaving a size of approximately 1" x 4 x /8, and a surface area ofapproximately 58 square centimeters. The specimens were abraded through40 emery paper, degreased in benzene, and washed in distilled water.Immediately after drying, the specimens were weighed and placed in acorrosion cell and immersed in the corrosive solution. Each of thecorrosive solutions, except those used for control purposes, contained apredetermined concentration of methyl betanaphthyl ketone. The amount ofcorroded metal was determined by weight loss. The corrosion cell wasbasically a 2000 m./l. Erlenmeyer flask with a special top to permitentrance and exit of nitrogen for deaeration and to prevent aircontamination. The cell had a removable chimney with Pyrex hooks fromwhich the metal specimens were suspended. The corrosive solution wasdeaerated with nitrogen before each run. Nitrogen also was bubbledthrough the solution continuously during a run to prevent contaminationwith air. A constant temperature was achieved by the use of a constanttemperature oil bath. All runs were carried out for 2 days at a constanttemperature of 25 C.

The results of representative experiments utilizing the above procedureare summarized below in Table I. In this table, corrosion rate inmilligrams per square decimeter per day (mg./dm. /day or m.d.d.) andpercentage inhibitor efficiency (which equals where L, is the corrosionrate without inhibitor and I is the corrosion rate with inhibitor) aregiven for various concentrations of inhibitor in moles per liter(m./l.).

TABLE I Inhibitor con- Corrosion Percent centration, rate, inhibitorm./l. mg./drn. /day efficiency Blank 1, 555 l0- 904 41. 6 5 l0- 627 66.1 10" 500 67. 8 10- 572 63. 2

Example 2 The protective properties of methyl beta-naphthyl ketone forinhibition of corrosion of 1020 carbon steel in a hydroformerregenerator circuit condensate at 212 F. was determined according tothis example. The condensate is a highly corrosive acidic substancehaving a pH of 0.5. The procedure followed was the same as in Example 1.Results are given in Table II.

TABLE II Inhibitor con- Corrosion Percent centration, rat inhibitorm./l. mgJdmfl/day efiicieney Blank 41,114 10 17, 229 58. 1 10- 16, 24260. 3

where R is a lower alkyl radical containing from 1 to about 4 carbonatoms.

2. A process according to claim 1 in which the compound is methylbeta-naphthyl ketone.

3. A process according to claim 1 in which the metal is a ferrous metal.

4. A process according to claim 1 in which said solution has a pH notgreater than about 4.

5. A process according to claim 1 in which said corrosion inhibitingcompound is present in a concentration of about 10- m./l. to about 0.5m./l. in the aqueous acidic solution.

6. A process according to claim 1 in which said acidic solution is acondensate in a hydrocarbon process stream.

7. A process according to claim 1 in which said corrosion inhibitingcompound is added to a hydrocarbon process stream upstream of the areato be protected.

8. A process for inhibiting corrosion of a metal by an aqueous acidicsolution which comprises adding to said solution a small but effectiveamount of a corrosion inhibiting compound having the formula ArCR I;

where Ar is an alpha-napthyl or beta-naphthyl radical and R is a loweralkyl radical containing from 1 to about 4 carbon atoms, said solutionbeing surrounded by an inert or reducing atmosphere.

9. A process according to claim 8 in which Ar is betanaphthyl.

10. An aqueous acidic solution inhibited against corrosive attack onmetals, said solution consisting essentially of an aqueous acid normallytending to cause corrosion of metals, and a small but effective amountof a corrosion inhibiting compound having the formula where R is a loweralkyl radical containing from 1 to about 4 carbon atoms.

11. A solution according to claim 10 having a pH not greater than about4. I

12. A solution according to claim 10 in'which said compound is presentin a concentration of about 10" m./l. to about 0.5 m./l. I

13. A solution according to claim 10 in which R is methyl.

14. A solution according to claim 10 in which said compound is methylbeta-naphthyl ketone.

15. A solution according to claim 10 in which said acid is hydrochloricacid.

References Cited UNITED STATES PATENTS 2,430,058 11/1947 Klaber 252 3963,493,510 2/1970 Chao 252 -396 OTHER REFERENCES H. H. Uhlig, TheCorrosion Handbook, J. Wiley, 1948, pp. 910, 911, and 912.

RICHARD D. LOVERING, Primary Examiner I. GLUCK, Assistant Examiner

